For a constant Hubble constant H0 (to simplify things) and distance r, your proper acceleration due to Hubble flow should be a=H02r, right?

Suppose your mass is 70 kg and your duck's mass is 1 kg. The distance at which your mutual gravitational attraction (G*(71 kg)/r^2) equals and opposes your recessional acceleration (H02r) is 3√(G*(71 kg)/H02). Using a value of H0=67 (km/s)/Mpc, this gives a distance of 1.0 × 106 km, or 2.6 times the average distance to the Moon. This surprisingly small distance makes sense given how weak the gravitational force is between you and your duck. At a distance of a million kilometers, it is a mere 4.7 × 10-27 N, equivalent to the electrostatic force between a proton and an electron 22 cm apart.

If you already watch Space Battleship Yamato 2199, or at least heard of this by name, you guy probably know what I was going for, but I'll explain it for those who don't:

In the remake, the Wave Motion Gun fire by compressing thing into a micro black hole, then used the Hawking Radiation that's coming out of it for destructive effect. So, assuming I want to build this in a form of a Sniper Rifle, have the same Indestructium that could reflect any type of radiation and already a way to compress and create micro black hole on a fly, how should I build it?

Well obviously. I mean the central design. One of the advantagous of this kind of gun is that you could be really versatile about the material used as the bullet, so you could have the gun not having a magazine, instead sucking air from the surrounding, store it temporaly, and then suddenly compress them to fire.

andykhang wrote:If you already watch Space Battleship Yamato 2199, or at least heard of this by name, you guy probably know what I was going for, but I'll explain it for those who don't:

In the remake, the Wave Motion Gun fire by compressing thing into a micro black hole, then used the Hawking Radiation that's coming out of it for destructive effect. So, assuming I want to build this in a form of a Sniper Rifle, have the same Indestructium that could reflect any type of radiation and already a way to compress and create micro black hole on a fly, how should I build it?

andykhang wrote:Well obviously. I mean the central design. One of the advantagous of this kind of gun is that you could be really versatile about the material used as the bullet, so you could have the gun not having a magazine, instead sucking air from the surrounding, store it temporaly, and then suddenly compress them to fire.

Oof, talk about running before you can walk.

There is too much fantasy to give a better answer than "just build it smaller". Its super-over-the-top tech, there is no discussion about "materials" because we know it must be made with equal parts unobtanium, handwavium and indestructium. There is no discussion about design because we know that none of human knowledge can describe such a machine. Its like asking what size screws to use in a warp drive -> Any size you want.

What you describe is essentially a matter-energy-conversion-powered x-ray laser. So all you have to do is type "matter-energy-conversion-powered x-ray sniper laser" and you're done

So, with the railgun finally somewhat ready for practical used, and soon to be put on a battleship, soon enough there're going to be some crazy design surrounding this (prefertively the Japanese, but they put all their crazies in their culture nowaday), so I thought I would suggest one such design and see how it work:

Supposedly I want to build a destroyer, built-in with Railgun technology. I was planning to do that by, instead of needing large source of electrical power, I just build a railgun long enough to compensate that. Supposedly then, I achieve that by building it inside the destroyer itself, placing it along the length of the ship from stern to bow, escaping out of it, essentially making what the Nazi were doing with their railway gun (or for Anime reference: the Yamato's Wave Motion Cannon low-tech, more realistic cousin). Supposedly that work, how much electrical power, then, do I need to fire a 100mm tungsten steel bullet at mach 6? (supposedly that the destroyer was 120m long)

Second, would it be practical, with modification to what I was suggesting? And for what? I imagine it would be a primary weapon for the destroyer for longshot sniping at critical part of a warship or onshore instalation, but that just my butt talking.

andykhang wrote:So, with the railgun finally somewhat ready for practical used, and soon to be put on a battleship, soon enough there're going to be some crazy design surrounding this (prefertively the Japanese, but they put all their crazies in their culture nowaday), so I thought I would suggest one such design and see how it work:

Supposedly I want to build a destroyer, built-in with Railgun technology. I was planning to do that by, instead of needing large source of electrical power, I just build a railgun long enough to compensate that. Supposedly then, I achieve that by building it inside the destroyer itself, placing it along the length of the ship from stern to bow, escaping out of it, essentially making what the Nazi were doing with their railway gun (or for Anime reference: the Yamato's Wave Motion Cannon low-tech, more realistic cousin). Supposedly that work, how much electrical power, then, do I need to fire a 100mm tungsten steel bullet at mach 6? (supposedly that the destroyer was 120m long)

Second, would it be practical, with modification to what I was suggesting? And for what? I imagine it would be a primary weapon for the destroyer for longshot sniping at critical part of a warship or onshore instalation, but that just my butt talking.

Merely the fact that it can only be aimed by pointing the whole ship and elevation will be severely restricted limits the practicality of this weapon.The elevation restriction alone will reduce range by orders of magnitude. A hypothetical modern railgun weapon would fire almost straight-up for max range, lofting a guided projectile above most of the draggy atmosphere - a horizontal, sea-level shot will have terrible range.

SBS Yamato was after all, a spaceship and well...not a practical real-world design to base practical, real-world speculation on.

As for power requirements, well warships tend to have plenty of power, and you would be using capacitors (or whatever cutting-edge equivalent) to "charge up", so pure power output [of your powerplant] won't be so much the limiting factor as much as your storage and release capacity would be. Power output will affect theoretical max rate-of-fire, but I dont really see that being an issue.

Its also worth noting that the Nazi's railways guns saw very limited use for much the same reasons - they were immensely unwieldy and could only be aimed effectively with weeks of preparation. And you could achieve a far greater destructive effect with an equal amount (in terms of cost and manpower) of conventional artillery. Or say, a small number of airborne bombers.

The railway guns, and the Paris gun, and the V3 gun, were abberations that were obsolete almost before they were finished.

Yeah...and designing it so that the gun will aim straight up would definitively capsize the thing immediately after the first shot unless you planned to have atleast have at least half of the entire gun be submerge underwater (in this case you would actually be better build it as a submarine anyway), if the force haven't break the thing in 2 yet. That's a shortcoming I never see it coming, as shorter range mean significantly weaker power when travel longer, rendering the entire point of this thing significantly more useless.

Still, it being a destroyer would make it more useful than the railway gun, since it can actually turn and is actually more advantagous to point bow-in into a supposedly helpless ship, I think.

So I calculate the kinetic energy of this thing to be about 420 million Joules in the bullet upon firing. With that much energy, how long is it range, supposedly I aim it at sea-level?

andykhang wrote:So I calculate the kinetic energy of this thing to be about 420 million Joules in the bullet upon firing. With that much energy, how long is it range, supposedly I aim it at sea-level?

At sea-level? Surprisingly low. One needs more data in order to take an appropriate guess, but due to the thickness of the atmosphere at sea-level and with drag being proportional to the square of velocity, in those conditions, adding more power gets you diminishing returns. Do not underestimate how hard it is to push atmosphere out of the way at hypersonic speeds.

A guess based purely on my gut, would be somewhere in the region of 10miles, give or take 5miles.

It certainly wont be as far as 100miles and it certainly will be further than 1mile.

***

Side-note: there just isnt a simple equation to calculate range from a few facts about the projectile, it will travel through the supersonic and hypersonic regimes where aerodynamics gets...weird & non-linear.

***

Quite apart from the fact that air resistance at sea level is catastrophic at these speeds, with low elevation the projectile just isnt going to get the height to travel very far, ballistically.

At sea-level that 420MJ will rapidly be dumped as heat into the projectile and the atmosphere, and FYI 420MJ is sufficient to vaporise roughly 90kg of tungsten. Of course not every single Joule of that 420MJ will end up as heat in the projectile, far from it, but its illustrative.

When penetrating a material (be it solid steel, or 10km of air) with a fast projectile, above a certain energy, adding more energy to the system does not increase penetration, but increases the power of the energy release at impact. (In this context, "penetration" and "impact" both refer to the projectile travelling through air - think of impact occurring at the muzzle and "penetration depth" being range.)

andykhang wrote:I achieve that by building it inside the destroyer itself, placing it along the length of the ship from stern to bow, escaping out of it, essentially making what the Nazi were doing with their railway gun (or for Anime reference: the Yamato's Wave Motion Cannon low-tech, more realistic cousin). Supposedly that work, how much electrical power, then, do I need to fire a 100mm tungsten steel bullet at mach 6? (supposedly that the destroyer was 120m long)

andykhang wrote:I calculate the kinetic energy of this thing to be about 420 million Joules in the bullet upon firing. With that much energy, how long is it range, supposedly I aim it at sea-level?

"Supposing that the destroyer is 120m long," not "supposedly that ... " and "definitely," not "definitively." A definitive thing is the example that gives the word its meaning. When you just want to say something's beyond doubt, say "definitely."

You didn't say, so I worked it out.Assuming linear acceleration (which is what gets you 0-30 mph in 1.5 seconds, 0-60 mph in 3 seconds, 0-90 mph in 4.5 seconds, 0-120 mph in 6 seconds from a standing start to a quarter-mile downrange in sqr(90) seconds and upsided-down in a burning car with a broken leg at the first sharp bend if you're lucky*):

The French Rubis-class submarines have a 48 MW reactor that needs no refueling for 30 years.

No problem.

I do wonder just how you plant to mount this big bastard in your ship. Recoil's a bitch, right?

Also there's the point others have made, that adding velocity at the muzzle makes less and less difference a mile downrange. The velocity-range graph for a bullet is a curve:

Getting from 400 J to 600 J buys you an extra 130 m of range, but getting from 1200 J to 1400 J buys you only 70 m of extra range. A longer, heavier barrel and a larger powder load could knock that same bullet up to 2200 J, but you'd only achieve the same effect as moving maybe 40 m closer to your target ... which at 1 km range is ... ah ... 10 J?

There's a kink in the blue line just above 200 J, which is where a 62gr bullet drops below the sound barrier. There's less air resistance below the sound barrier.

The heavier projectile carries its energy down-range better. In other words you'd probably do better with a 400 kg projectile at 1443 m/s than with a 100 kg projectile at 2887 m/s. Unfortunately, you'd have to deal with twice as much recoil using the heavier, slower bullet.

Of course, there's another way to give your projectile some extra energy with which to make a mess of its target: fill it with explosives ...

... so it can fly 1000 km at more efficient subsonic speed then turn towards the target and increase speed for the final charge.

Velocity to barrel length is also a curve, but with full-bore rifle ammo nobody wants to carry a rifle long enough to get even 90% max velocity anyway. .22 and 9mm max out at sensible carbine barrel lengths but for .308 Winchester:

* If you're unlucky you land outside the car with a broken spine and get to watch it burning on top of what used to be the school bus queue, then and every night for the rest of your life.

Adding electronic to a railgun sound like a pretty bad idea for me though, unless you got perfect insulation. The weight of a bullet itself is also a problem, as 400 kg is probably a sizable chunk of the ammo capacity for regular destroyer, but it could make it up with it one-shot-kill potential.

Otherwise, pretty good. As for the recoil, either I make this parralel and inside the ship itself so that it can only go backward, or I make it so that part of the cannon is submerge underwater, and ultilizing the drag there. As for the later, it being a submarine would be better for it.

Speaking of submarine...you said that it have a 48MW generator right? What happen if I have that same length, but charge it with at least half of it power, and aim at point-blank range toward a battleship? (since you definitively wouldn't aim far with this)

If you shoot it level then how long does it take the projectile to fall? Unless what little I remember of my physics is wrong, if you fire with no elevation the projectile will hit the ground in the time it would take a weight to fall that distance. Which is why cannons are never fired that way. And what is the point of putting a rail gun on a submarine? It has to be at the surface to fire and that gives up the advantage of being a submarine in the first place. And are there any operating battleships in the US fleet?

I said battleship,but this thing would be more likely to aim at either aircraft carrier or on-shore installations, or pretty much any static target. And the reason Sub is better because that thing is supposed to be fired from long away anyway, where it would be hidden from sight and be fire tilted with only it head poking out ( or the cannon’s head if build at the middle and be able to tilted independently from the sub) before ducking back down again. This’s basically a snipe weapon to begin with

andykhang wrote:Adding electronic to a railgun sound like a pretty bad idea for me though, unless you got perfect insulation. The weight of a bullet itself is also a problem, as 400 kg is probably a sizable chunk of the ammo capacity for regular destroyer, but it could make it up with it one-shot-kill potential.

Otherwise, pretty good. As for the recoil, either I make this parralel and inside the ship itself so that it can only go backward, or I make it so that part of the cannon is submerge underwater, and ultilizing the drag there. As for the later, it being a submarine would be better for it.

Speaking of submarine...you said that it have a 48MW generator right? What happen if I have that same length, but charge it with at least half of it power, and aim at point-blank range toward a battleship? (since you definitively wouldn't aim far with this)

Sableagle wrote:... and "definitely," not "definitively." A definitive thing is the example that gives the word its meaning. When you just want to say something's beyond doubt, say "definitely."

Sableagle wrote:... and "definitely," not "definitively." A definitive thing is the example that gives the word its meaning. When you just want to say something's beyond doubt, say "definitely."

Sableagle wrote:... and "definitely," not "definitively." A definitive thing is the example that gives the word its meaning. When you just want to say something's beyond doubt, say "definitely."

The problem with recoil isn't just that it's going to *move* the ship. The problem is that it's going to *suddenly accelerate* the ship *by a small part*.

For comparison, the old QF 4 inch gun Mk XVI lobbed a 15.88 kg HE shell at 811 m/s with 12880 kgm/s of momentum.

A Type 45 is about 8000 t or 8000000 kg. That 400 kg bullet's momentum must be offset by equal and opposite momentum sufficient to send that ship backwards at 13.86 m/s, or 27 knots. That ship's max speed is "over 30 knots." For the 200 kg bullet it's 9.8 m/s, equivalent to a full second in freefall aka being dropped 5m nose-first onto a cannon that's fixed in position. For the 100 kg bullet, it's 6.93 m/s, which is still 15.5 mph, so a 1 hr 41 min 30 sec marathon time. That momentum is being transferred to the ship in 0.11 seconds.

Assuming you have a crew on board this thing, either they're strapped in and accelerating at 126 m/s^2 or they're slapped by a bulkhead that's going at 13.86 m/s. Neither of those things is going to be good for them.

If you want to use it from extremely close quarters on board a submarine against an aircraft carrier, firing nearly vertically upwards, you're firing from *under* the carrier and you've got to clear the seawater from your barrel first or there will be problems and you'll only hit that water, not the carrier.

If you want to use it as a howitzer, lobbing shells into Pyongyang from somewhere off Petropavlovask or Davao, you've still got the recoil to consider. Yes, the water's in the way. Yes, that will stop you from going *thud* on the sea floor 1km down 72 seconds after you fire. Yes, buoyancy will keep your boat afloat if it's made of adamantium. Your problem is that it's not made of adamantium.

Here's a 90kg boat. It might well survive a 5m bellyflop. Imagine that's floating on the water, happy as a boat can be, and a 90kg man drops 5m into the middle of it, though. Think he's going to bounce the boat a little and go on with his life, break his legs or punch right through the hull and wreck the thing? Snapping your submarine at the middle is not a good idea.

So in other word, I need to ridiculously afix this thing in place, or let the cannon move freely to an extend to minimize the recoil...That would either further limit the way this thing would work, or we're forced to lower the power instead.

...Come to think of it, if you need an entire island to afix your ship cannon, better make it a stationary cannon instead. (Or alternatively, creating underwater large "fins" to spread the recoil to a large area, and let the cannon move into the water itself, independence from the movement of the ship)

Still doesn't answer my question though. I imagine that the ship's going to be split in 2, but what happen after that?

Edit: Then again, there's also the problem of the ship's durability itself...

No. You can use it the way the Navy will, as a replacement for its 5 inch guns. Or you can launch aircraft like on the newest carrier. You could use a variant to replace the 16 inch guns that were on the Iowa class battleships. But why would you? If you are fighting other ships missiles can hit over the horizon and sink anything you can see. Which means a small ship can sink a battleship. Seems a poor trade. And the ships can launch cruise missiles which have longer ranges than almost any kinetic weapon.

Submarines are designed to operate deep and by stealth. Not to do cannonade work at the surface. They are expensive. Again its cheaper to use smaller boats and missiles, or aircraft and missiles. If you want to launch rocks go to the moon and build your rail gun there. Send rocks in steel jackets. You can hit almost anything anywhere with kinetic strike weapons with outputs similar to nukes. And pretty much unstoppable. If you want to go full on scary put nukes in reentry vehicles in orbit, By the time you see them you won't have much time to kill them.

Killing technology is pretty much at its nadir. We don't need better. And space battles aren't ever going to happen like navel battles did. If you read this, and if it is true, then it should make my point.

morriswalters wrote:Killing technology is pretty much at its nadir. We don't need better.

We're nowhere near the nadir.

The direction of travel won't be to make explosions bigger and more spectacular, that's true; Instead, weapons will do the same or lesser damage but be miniaturised and much better targetted. Eventually every Tom, Dick or Mohammed will possess the capacity to decimate the human race - whether that's with a GM virus, a pack of self-replicating nanobots, or simply a computer virus that melts all our brains which are now hardwired into the web 12.0

Before all that though, sadly, autonomous killer drones and robots are almost inevitable at this point: It will become politically unacceptable to send citizens to their deaths in war when automatons could go in their place; In addition, said automatons will be cheaper, more efficient, better at following orders, much easier logistically, and so on.

Of course, said killer robots might also come with one or two downsides as sci-fi has taught us...

I think, long story short: Giant railguns do not equal giant war fighting capability and are probably inferior to a battery of smaller weapons.

Look at the Tsar Bomba:

Biggest nuke in the world.No delivery system powerful enough to deploy it.Much greater destruction can be wrought with a group of much smaller weapons due to inverse-square law so nobody bothered trying to build one.

Ergo - while more "powerful" weapons can be built in many areas, they are not necessarily "better" weapons and can be much worse.

Size & power are not the only factor in deciding weapon effectiveness. There are no variables that can be increased arbitrarily for a proportional increase in effectiveness, at some point, all variables result in diminishing returns and even decreasing benefit.

Just like a torpedo is not suitable for use on tanks, a giant railgun is better suited for space. On land, it is a propaganda tool.

Yeah...so this design is kinda like the Yamato or the Bismacrk: A thing built mostly for propaganda, only for it to work too well and sunk too early to do any significant damage. Only that this thing is even less realistic lol (Seriously, it somehow is better as a kind of mobile marine artillery than it's being an actual warship)

andykhang wrote:Yeah...so this design is kinda like the Yamato or the Bismacrk: A thing built mostly for propaganda, only for it to work too well and sunk too early to do any significant damage. Only that this thing is even less realistic lol (Seriously, it somehow is better as a kind of mobile marine artillery than it's being an actual warship)

andykhang wrote:What happen if you concentrate all the energy the Sun have to accelerate a single electron? Would it become a black hole traveling at near-light speed?

It wouldnt form a black hole because its not gaining "real" mass (if you were co-moving with it, its mass would not appear to increase, so how would a BH form? It doesnt, apparently) but to a stationary observer, I think you would feel the effect of an increased mass passing by.

Well, if that thing didn't already break the law of physics as we know it and the time and length dilation math still work, that thing would be a point energy (magnitude) smaller than a planck scale, and would outlive the sun before it even decay (check your math, you know it to be true).Also, nothing short of a black hole could stop it, and I haven't even calculate what happen if that thing hit the earth right at the center yet